ch1 products from crude oil

7/30/2019 CH1 Products From Crude Oil

1/17

Cracking

Short alkane chains from Fractional Distillation (used e.g. for petrol) are in much

greater demand than long chains.

This means that after fractionation, there are long chains left over when all theshort chains have been sold.

To make most efficient use of the crude oil, these long

chains are cracked in the refinery.

Cracking produces SHORTER CHAIN ALKANES plusmolecules called ALKENES

The shorter chain alkanes help satisfy the demand

for short chain fractions to be used as fuels.

Alkenes are important starting points for manyproducts made in the chemical industry e.g. plastics,

pharmaceuticals.

Cracking is a THERMAL DECOMPOSITION reaction

the long chains are heated until vapourised and the

vapour is then passed over a hot catalyst.A catalytic cracking plant


2/17

What are alkenes ?

Recall that the alkanes are a family of hydrocarbons.

The alkenes are also a family of hydrocarbons, but they have a double bond

between two of the carbon atoms. This means that

i) they are unsaturated

ii) they have a general formula Cn

H2n

Having a double bond means that alkenes are more reactive than alkanes which is

why they are so useful as starting points for making other chemical compounds.

Here are displayed formulae for some alkenes:

H H HH | | |

C = C C C H

H | |

H H

H H

C = C

H H

H HH | |

C = C C H

H |

HEthene C2H4 Propene C3H6 Butene C4H8


3/17

Cracking reactions

The number of carbon and hydrogen atoms always has to add up to the same on

both sides of the equation always check to make sure this is so !

e.g. octane hexane + ethene

C8H18 C6H14 + C2H4

decane heptane + propene

C10H22 C7H16 + C3H6

Sometimes a chain may crack twice two alkenes will be formed

e.g. decane propane + butene + propene

C10H22 C3H8 + C4H8

+ C3H6

Hydrogen can also be made as a product of cracking

e.g. hexane hexene + hydrogen

C6H

14 C

6H

12+ H

2


4/17

Telling an alkane from an alkene

The test for a compound which contains one (or more) double bond between carbon

atoms is to shake the compound with bromine water

If the compound is unsaturated (contains a double bond) then the bromine water

reacts with the alkene. The bromine water turns from orange to colourless. We say

that the alkene decolourises bromine water.

If the compound is saturated (no double bonds) the bromine water cant react with

it, and the bromine waterremains orange.

Testing an alkane and an

alkene with bromine water

After adding bromine water and

shaking


5/17

The alcohol (called ethanol) in both of these products has

been produced by a chemical reaction (its the same

alcohol we might find in wine, or beer). While the alcohol is

the same, the reactions are very different.

You will need to be able to compare the two routes by

which ethanol is made.

Industrial ethanol

made by the

reaction of

ethene withsteam

Ethanol as an

alternative fuel

made by the

fermentation of

plant matter


6/17

Making ethanol from ethene

When heated and treated with a catalyst, ethene reacts with steam to produce

ethanol. The equation for the reaction is:

H H H H

| | | |

C = C + H-OH H C C H

| | | |

H H H OH

ethene + water ethanol

C2H4 + H2O C2H5OH

The ethene is obtained from cracking of long chain fractions from crude oil. It istherefore from a non-renewable source.

The reaction goes at high temperature, so there are high energy costs

The reaction can carry on as a continuous process, so large amounts of ethanol

can be made relatively quickly this way.


7/17

Making ethanol by fermentation

Plant matter containing sugars (build up by the plant during photosynthesis) can be

fermented using yeast. The yeast organisms convert the sugars into ethanol and

carbon dioxide.

sugars ethanol + carbon dioxide

C6H12O6 2 C2H5OH + 2 CO2

The process uses plant matter which can be

regrown continuously, so its from a renewable

source

The process does not require high temperatures

low energy costs

The yeast dies from ethanol poisoning, so the

process has to be stopped and the ethanolextracted and purified before starting over again

with fresh yeast. This is called a batch process.

The reaction is slow. It takes a long time to make

ethanol by this route compared to the industrial

route.


8/17

Plastics are made from molecules which have extremely long chains of carbonatoms. We call these molecules polymers. They are made by linking together

huge numbers of much smaller molecules to form the chain.

Alkenes are suitable molecules to use for these polymerisation reactions.

Common plastic materials such as

polythene

polypropylene

PVC

Perspex

are all polymers made from alkenes

Manufacturing large polythene bags


9/17

A polymer molecule is made by reacting together many smaller molecules to link

together into a chain. These smaller molecules which form the chain are called

monomers.

Polymers are named by taking the monomer name, putting it in brackets, andadding poly in front.

e.g. The polymer made from ethene is

called poly(ethene) known by the

common name polythene

Alkenes are one type of monomer which link togetherto form polymers. The reaction is called addition

polymerisation, because the monomers add on to one

another to form the chain, and no other product is formed.

It would be impossible to draw the whole of a polymer

molecule its too long ! Fortunately a polymer chain

contains the same arrangement of atoms repeated over

and over again. Instead we can draw a repeat unit, or

a section of the polymer.

Products made from

poly(ethene)


10/17

Look at these monomers, and see how the polymer repeat unit and structure are

drawn using DISPLAYED FORMULAE:

Monomer Repeat Unit Section (showing 3 repeats)

H H H H H H H H H H

| | | | | | | | | |

C = C C C - C C C C C C -

| | | | | | | | | |

H H H H n H H H H H H

ethene poly(ethene)

H H

H C| / H

C = C

| |

H H

H H

H C| / H

C C

| |

H H n

propene poly(propene)

H CH3 H CH3 H CH3| | | | | |

- C C C C C C -

| | | | | |

H H H H H H

poly(ethene)

poly(propene)


11/17

Points to remember when drawing polymers:

1) The polymer is formed by breaking open the double bond and using it to join to

monomer molecule either side. This means that every repeat unit is a section of

the chain two carbon atoms long.

2) The double bond is broken when the polymer is made, leaving just single bonds.

There are no double bonds in the repeat unit or section

Balanced equations:Chains are different lengths, made from differing numbers of monomers. The best we

can do is to say there were n monomers joined together to make the chain.

The balanced equation therefore is written as: (note where the n s are)

Cl H

| |

C = C

| |

H H

Cl H

| |

C C

| |

H H

n

n

n monomers join

together to form a

polymer which is n

repeats long

chloroethene poly(chloroethene)


12/17

AdvantagesAdvantagesandand

disadvantagesdisadvantagesofofusing products fromusing products from

crude oil as fuels or ascrude oil as fuels or as

raw materialsraw materials

Fossil fuels contain a little sulphur

which, when burned, forms sulphur

dioxide this causes acid rain.

Crude oil is a non-renewableresource, taking millions of years

to form it is a finite resource.

Products from crude oil provide

valuable starting points forchemicals such as life-saving

drugs and high-tech polymers.

The economies of the

industrialised world are

dependent on oil supplies.

Rapid transport and

available electrical power

underpins our society.The main gas implicated in Global

Warming is carbon dioxide one of the

products of burning fossil fuels.

Fuels such as petrol and

diesel are easy to transport,

relatively safe to use,

Alternative fuels are not yet

sufficiently safe, cost effective or

capable of meeting the massive

energy needs of modern society, but

fossil fuels are available in sufficient

supply to meet current needs.


13/17

At first when a new polymer was discovered, Scientists thought long and hard about

what jobs these polymers could do. Some polymers, such as the adhesive on Post-It

notes, were happy accidents !

Modern scientists understand polymers and how to make them very well. Now

polymers are designed with specific properties to do well-defined jobs. There might

be called Designer Polymers.

Polymers designed for specific jobs include:

Kevlar - designed for body armour- very strong but lightweight

Lycra - sports-wear

- very flexible but strong

Goretex - breathable fabric- lets sweat out but prevents

rain getting in


14/17

Designer polymers have made an impact in medical applications too:

Smart Materials are materials which

change in response to changes

around themselves.

Shape memory polymers can change

their shape in response to heat.

Stitches which can pull the edges of a

wound together at body-temperature

are one example.

Hydrogels contain cross-links which trap

water, making wound dressings which are

moist and sterile possible, as well as being

useful for soft contact lenses.


15/17

Remember !

Polymers are made from monomers such as alkenes

Alkenes are made by cracking reactions, along with

short chain alkanes the starting material is long-chainalkanes

These long chain alkenes come from fractional

distillation of crude oil

Therefore polymers of this kind are from non-renewable sources, and are using up our crude oil

reserves.

RECYCLING helps to reduce the rate at which crude oil

is used up to make polymers. BUT recycling is labour

intensive, and the different polymers all have to besorted. Therefore recycling plastics is not very cost

effective.

Many people cant be bothered to save and sort plastic

waste for recycling.


16/17

Many polymers are not bio-degradable.This means that they will not be broken

down in nature by micro-organisms.

This causes problems for disposal of waste polymers:

- because they dont bio-degrade they can take up valuable landfill

- they may give offtoxic fumes when burnt

- plastic waste is unsightly and can be dangerous to wildlife, if animals

or birds swallow the plastic, or get trapped in waste objects

- recycling takes a lot of effort to collect the waste

- to recycle the plastics have to be sorted into different types, which is

labour intensive and an unpleasant job- for these reasons recycled plastics can be more expensive than just

making new polymers using products from crude oil


17/17

What are scientists doing to solve polymer disposal problems ?

Designing polymers which are bio-degradable,

or photo-degradable (broken down slowly bysunlight),

or water-soluble.

Developing ways of burning plastic waste as a fuel

but without the toxic emissions, e.g. by using

scrubbers to remove these gases.

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